Background imagery is "donated" by companies such as DigitalGlobe and Bing. We have no control over how often they update their imagery. Furthermore, I can imagine that the Chinese government is not really cooperative and might even forbid recent imagery.

More info on mapping in China and what is allowed there, can be found on the wiki

If you are not aware of it: you can chose between different background images. With the in-browser editor ID you can do so from the layers menu on the right screen edge. Maybe you find one image layer that is more up to date.